An electrical power line insulator having an end clamp is usually used to support an electrical wire of a distribution line. After the electrical wire is seated in a saddle, a keeper is moved in a track to tightly engage and support the outer portion of the electrical wire.
Electrical power line insulators having such end clamps have been developed using various technologies over several decades. Recently, in order to enhance the safety and convenience of installation, technologies improved in various ways have been suggested.
Electrical power line insulators are classified either as separated-type or integrated-type. A separated-type electrical power line insulator is constructed so that an end clamp for supporting an electrical power line and an insulator housing mounted on a support structure, such as a cross arm of an electric pole, are manufactured separately and are then assembled with each other. An integrated-type electrical power line insulator is constructed so that an end damp and an insulator housing are integrated into a single structure.
In the separated-type electrical power line insulator, an extension leg of the end damp supporting an electrical wire is connected to a fitting part provided on the upper portion of the insulator housing. By tightening a bolt which passes through the insulator housing so as to be opposite the fitting part, the end clamp is attached to the insulator housing.
In such a separated-type structure, the end clamp can be freely rotated because of an annular groove which is cut on the outer circumferential surface of the extension leg, when the bolt of the fitting part is loosened to some extent, thus freely accommodating the distribution direction or angle of the electrical wire, therefore being convenient to use. However, the separated-type structure is problematic in that the bolt must be securely tightened after the installation. A safety device for preventing the bolt from coming loose is unsatisfactory.
In other words, the separated-type structure is problematic in that, even if the bolt fastening the end clamp to the insulator housing is firmly tightened, after a long period of time passes following installation, the electrical wire is repeatedly shaken by external forces, such as strong wind, thus causing the insulator to vibrate, therefore loosening the bolt. Consequently, the end clamp moves while rotating freely, and consequently an end portion of the saddle of the clamp applies shearing stress to the electrical wire in the distribution direction thereof, thus causing an accident such as breakage of the wire.
Therefore, recently, the integrated-type electrical power line insulator, that is a one-piece-type electrical power line insulator constructed so that the extension leg of the end clamp and the insulator housing compress and secure the post to be integrated with each other, has been suggested.
However, a one-piece-type insulator has several drawbacks compared to a separated-type insulator. Problems with the one-piece-type electrical power line insulator will be described below.
Firstly, a one-piece-type insulator is problematic in that, when either the end clamp or the insulator housing is partially damaged, the end clamp or the insulator housing cannot be separated from each other, so that the entire insulator must be replaced with a new one.
During or after installation, damage to an electrical power line insulator, for example damage to the saddle of the end clamp, damage to the insulator housing due to careless handling during installation and transport, tearing caused by the beak of a bird, such as an eagle or a hawk, or damage to insulating rubber caused by alkalinity of coastal areas, leads to interruption of the electric current. In order to respond to such an incident, the entire insulator must be replaced with a new one. This is very inefficient in terms of economics.
Secondly, a one-piece-type electrical power line insulator is problematic in that it is difficult to tighten a conductor (electrical power line).
A one-piece-type electrical power line insulator is installed as follows. An auxiliary working tool (eyenut) is assembled with a protruding end of a bolt fastening the saddle of the clamp to the keeper moving in the clamp, and a working tool, such as a pulley, is connected to the auxiliary working tool. The electrical wire is then raised up and is seated in the saddle using the pulley. Next, a worker must promptly tighten the bolt. However, the working tool must be removed before it is possible to tighten the bolt. This is inconvenient and inefficient in terms of time.
Thirdly, a one-piece-type electrical power line insulator is problematic in that corrosion may cause a structural problem related to the saddle receiving the keeper, so that a long life span is not ensured.
In a one-piece-type electrical power line insulator, the lower portion of the track guiding the keeper is closed, so that water collected in the track is not drained, and the collected water causes corrosion of the clamp. Especially in coastal areas having high alkalinity, corrosion proceeds quickly. Thereby, insulating performance is lowered due to breakdown, and the life span of the insulator is reduced.